Theme 1: The immune system Flashcards
The main differences between innate and adaptive immunity
- Innate: first line of defence. Rapid
-Basic level of protection
-Fixed
-constant during exposure
-Limited specificity (reaction to all bacteria of a species)
-No memory
-Neutrophils
2.Adaptive
-Slow to develop
-Highly specific and respond to wider range of pathogens
-Variable
-Improves upon exposure
-Has memory. Long-lasting protection against infection. T cells, B cells, antibodies
Name and explain physical barriers of the body that prevent infection
1-Skin: keratin, high cell turn over, cell-cell junctions with small gaps and little intercellular material, low pH so inhibits growth of pathogens and favours immune cells.
2-Mucosal tissues: secrete mucous to coat bacteria and prevent attachment, ciliated epithelium so cilia eject bacteria, large surface area.
3-Saliva: lysozyme digest cell walls. Lactoferrin removes iron required by bacteria. Antibacterials. Fluid flushes out infection.
4-Urine - flush out pathogens
5-Acidic GI tract with digestive enzymes to inhibit cell growth
Give examples of when physical barriers to infection are compromised
1-Toxins from smoking can damage cilia in tissue
2- thickened mucous in cystic fibrosis can lead to lung infections (p. aeruginosa infection)
3-Burnt skin: removes epidermis which causes moist conditions and haem for bacteria. vascular damage inhibits chemotaxis
-Cuts allow opportunistic skin pathogens to enter (s. aureus)
-Surgery can cause sepsis: an excessive acute bacterial infection in the whole body
-Blockage of sebaceous glands and hair follicles can become infected
Why skin has low pH
-Fatty acids from sebaceous glands
-Lactic acid from sweat glands
Describe the role of commensal bacteria in host defence at mucosal surfaces
-In the gut, they stimulate colonic epithelial cells to give a balanced state called physiological inflammation
-Outcompete pathogens for nutrients, attachment sites and living space
-Some species can produce lactic acid (lactobacilli) and fatty acids (propionibacteria) which kill pathogens
What is the complement system and what 3 functions are involved
-it is a cascade that enhances antibodies and phagocytic cells to clear infection. Activated C3 convertase.
-Complement components are proteins in the blood and tissue fluid that cause:
1-Chemotaxis: recruitment of neutrophils to site of infection, causing inflammation
2-Opsonisation: coating bacteria to promote antigen uptake by phagocytes.
3-Membrane attack complex: AMPs disrupt the cell membrane and destroy the pathogen
What are antimicrobial peptides (AMPs) Where are alpha and beta defensins produced. Other example of AMPs
-defensins that kill pathogens at mucosal surfaces, by disrupting the cell membranes due to their amphipathic properties.
-⍺ - defensins: made by neutrophils and Paneth cells (epithelial cells in small intestine)
-β - defensins: made by epithelial cells
-lysozyme and phospholipase are also AMPs, made by Paneth cells
What 2 enzymes in tears and saliva digest i) bacterial cell walls and ii) cell membranes
i) lysozyme
ii) phospholipase
Paneth cells: where they are found, their function and what do they produce
-epithelial cells of the small intestine
-maintain integrity of gut function
-make a-defensins, lysozyme, and phospholipase
What are primary and secondary immune tissues and give examples
-Primary: produce immune cells in haematopoiesis.
-Bone marrow and thymus
-Secondary: sites where immune responses are initiated. Antigens are presented here.
-Tonsils, spleen, lymph nodes, Peyer’s patch, MALT
Explain the main process of haematopoiesis
-Pluripotent stem cell goes through the myeloid, lymphoid and erythroid lineages.
-Myeloid cell = Erythrocytes Platelets. Granulocytes. Monocytes which then make macrophages and dendritic cells
-Lymphoid cell: T cells. B cells (then plasma and memory) Natural killer cells
What is the thymus, its function and its main structure
-A primary immune tissue
-A bilobed organ above the heart
-T cells mature here and are activated before being distributed to secondary lymphoid tissue
-Has a fibrous capsule, with a cortex and medulla. Denser cells in cortex.
What is the lymphatic system. What are lymph nodes. And their different structural components.
-Lymphatic system – a system of capillaries, vessels and lymph nodes that transports lymph (extra fluid drained from cells and tissue) and returns it to the venous supply via thoracic duct
-Lymph nodes are secondary lymphoid tissues that contain immune cells to filter the lymph of any debris or pathogens picked up by diseased tissues
-Have a fibrous capsule defining the boundary of the node
- lymphoid follicles containing macrophages and lymphocytes where the immune responses take place
-Follicles have germinal centres for activation of T and B cells.
-Lymph enters via afferent and efferent vessels
What are Peyer’s patches. Structure and function
-A secondary lymphoid tissue
-M cells transfer pathogens into Peyer’s patch where it will be identified and generate an immune response by the loose cluster of WBCs beneath the epithelial surface of the small intestines
-destroy pathogens that have entered the gut
-Follicle structure, where immune response is generated. Has no fibrous capsule though.
What do tonsils do and their structure. What is characteristic of the tonsils.
-Lymphoid tissue that protect the airways (not the mouth)
-Waldeyer’s ring (palatal, lingual, pharyngeal, adenoids) at the entrance of the pharynx, larynx and gut.
-Underneath the epithelium, are the follicles of lymphatic tissues where the immune responses occur. And mucous-type salivary glands are beneath.
- Mucous type salivary glands are characteristic of tonsils.
-And microvilli with deep invaginations of epithelium to increase absorbance of nutrients
What are mucosa associated lymphoid tissue (MALT) Why it is so important
-system of small concentrations of lymphoid tissue found in various submucosal membrane sites(GI tract, nasopharynx, thyroid, breast, lung, salivary glands, eye, skin)
-Stimulated lymphocytes move between MALT sites rather than in the general circulation
-very important due to massive surface area of mucous membranes and high load of antigens from food/ air.
Structure and function of monocytes
-when they enter tissues, they develop into macrophages which phagocytose pathogens
-Curved horse shoe shaped nucleus. Few granules in cytoplasm
Structure and function of macrophages
-long living cells
-Large, some granules, round shape [kinda like a flower]
-Recognizes pathogens then releases cytokines to signal recruitment of neutrophils
to initiate inflammation
-Antigen presenting cells, activate T cells.
-Professional Phagocytes
-Scavenger cells – clear debris and dead cells
Structure and function of neutrophils. How are they recruited. Where they are stored
-large granulocytes, very granulated cytoplasm, multilobular nucleus, contain lysosomal enzymes and AMP.
-first responders in innate response. Short living. Most abundant WBC
-Stored in blood and bone marrow
-Neutrophil chemotaxis caused by cytokine signaling produced by macrophages, and complement components.
-influx causes swelling
-Professional phagocytes: engulf microbes by phagocytosis at infected sites to kill them
- are phagocytosed by scavenger macrophages
Structure and function of dendritic cells
-have dendrites so spidery structure
-Professional antigen presenting cells: present it in secondary lymphoid tissue to activate T cells and initiate an immune response
-Phagocytose
-Don’t clear infection
Structure and function of mast cells
-Lots of granules in cytoplasm
-Involved in mucosal immune defences
-Protect against parasites by releasing histamine, but can cause allergies
Stages of phagocytosis and what is the professional phagocytosers and other cells that can phagocytose
1-Recognition by receptors (antigen- complement receptors or receptors that identify antibody coated antigens (Fc) )
2-Engulfment – internalized into phagosome.
3-Phagosome acidified – kills most pathogens
4-Fuses with lysosome to make a phagolysosome.
5-degredation. Lysosymes destroy cell wall. Antigens then released
-Professional phagocytes= monocytes, macrophages and neutrophils
-Also dendritic cells and mast cells.
What cells signal the presence of pathogens to the adaptive immune system
Macrophages and dendritic cells
What are the professional antigen presenting cells
Dendritic cells, macrophages and B cells
What cells provide immunity to parasites
Mast cells, eosinophils and basophils
How immune cells can identify an antigen -The different types of receptors
-If it is coated in an antibody, Fc receptors detect this
-Complement receptors
-Pattern recognition receptors (PRRs) recognise pathogen associated molecular patterns (PAMPs)
Describe the main differences between the receptors in the innate and adaptive immunity. (specificity, if expressed in every cell type )
1-Innate receptors inherited so the same are expressed in every cell of a particular type.
-Adaptive develop their receptors during an immune response so different cells have different receptors
2-Innate triggers an immediate response unlike the adaptive
3-Innate recognise broad class of pathogens unlike adaptive
4-Innate cannot distinguish between different species, (eg. activated by all gram negative).
-Adaptive discriminate between closely related molecular structures
5-Innate has straight forward genetics. Adaptive make millions of proteins due to their high specificity and requires gene rearrangement. Encoded in multiple genes segments
What are pattern recognition receptors (PRR). Where they are found and on what cells. 3 examples of PRR. What do PRRs recognise
-The innate response recognises pathogens via PRRs.
-The receptors are membrane bound or in cytoplasm
-Found in macrophages, neutrophils, dendritic cells, epithelial cells.
-Toll-like receptors (TLR) and NOD-like receptors (NLR) and RLH receptors.
-They recognises and bind pathogen associated molecular patterns (PAMPs) (eg. peptidoglycan, LPS)
